Typically, the primary source of electrical power for a consuming entity, e.g. a telecommunications facility, is commercial power from a utility. However, for an off-grid or weak-grid telecom facility, the main power source may include an engine-generator set, such as a diesel generator, and a battery power source that can be used in backup situations. For example, if power from the commercial utility is lost, the diesel generator can be activated to supply power to the telecom facility. Start-up of the diesel generator, however, takes time; therefore, the battery power source provides power during this transitional time period. If the diesel generator fails to start (e.g., runs out of fuel, suffers a mechanical failure), then the battery power source is able to provide power for an additional period of time. Though diesel generators are inexpensive to install, the escalating cost of diesel fuel, and its delivery to remote locations, has driven the search for alternative, economical solutions.
For example, certain telecom facilities employ a diesel-battery hybrid power system to conserve fuel where the primary power source is a diesel generator. In such a scenario, a long, life-cycle battery is used to alternately share the site load with the diesel generator. More specifically, during operation, the diesel generator is modulated on and off and, when it is active, powers the facility and recharges the battery at an overall higher efficiency than if powering the facility alone. Once the battery is recharged, the generator can be turned off and the battery is used to sustain the facility load. Such hybrid power systems may also include a battery management system configured to monitor and control the battery.
Generally, telecom facilities include both direct current (DC) and alternating current (AC) loads. Typical AC loads at the site include, for example, the site air conditioning unit and lighting. The air conditioning unit maintains the site ambient temperature so as to ensure various equipment of the site operates with predetermined design limits. More specifically, the air conditioning unit is typically controlled via a separate controller having an internal thermostat. During operation, when the diesel generator is on and the battery is charging, the internal thermostat of the air conditioning unit controls operation of the unit to maintain the ambient temperature with predetermined limits. When the diesel generator is off and the battery is discharging, normal thermal loading from equipment at the site and/or from solar loading can increase the ambient temperature at the installed location (usually a small indoor shelter). During this time, once the temperature reaches a threshold temperature, the AC-powered air conditioning unit cannot turn on unless a DC-AC inverter is included in the power system because the diesel generator is off and the battery is DC-powered. Such an inverter, however, is typically very expensive and complex to install.
Accordingly, it would be advantageous to provide an improved system and method for controlling ambient temperature at a power-consuming site without installing an inverter.